Santourian



March 31, 1954 M. sAN'rouRIAN 1 MIscIBLE PHASE FLOODING N oIL PRODUCTION Filed April 2. 1962 MELCON SA NTOURIAN A TTORNE YS 3,126,951 MISCIBLE PHASE FLOODING IN OIL Y PRODUCTION Melcon Santourian, Bartlesville, Okla., assigner to Phillips Petroleum Company,a corporation of Delaware Filed Apr. 2, 1962, Ser. No. 184,279 16 Claims. (Ci. 166--9) This invention relates to a method of establishing a transition zone downhole around an injection well in a 'miscible uid drive process in recovering oil from an oilbearing stratum and utilizing this method in such a uid drive process to produce oil.

The need for a transition zone in a miscible uid ilood or drive' of a miscible fluid transition zone thru an oilbearing stratum to produce oil thru one or more produc- .tion wells is clearly taught in U.S. Patent 2,867,277 to toward the productionwells thereby producing oil in the production wells.

' This invention is concerned with 'a unique method of lforming' a better transition zone in the stratum around an injection well and to the use of this zone in displacing oil from the stratum by iluid drive.

Accordingly, itis an object of the invention to provide Van-irnproved method offorming a miscible phase transition zone in an oil bearing stratum around an injection well. Another object is to provide an improved transition zone which varies gradually in viscosity from the for-v ward areaadjacent the in-place oil to the area adjacent the injection well and in which the viscosity gradually varies substantially from that of the in-place oil to that of the miscible iluid utilized in forming the transition zone with the oil. -A further object is to provide an improved lluid drive process utilizing a'more eiiicient transition zone. Other objects of the invention will become apparent underconsideration of the accompanying disclosure.

A broad aspect of the invention comprises passing a fluid miscible with the in-place oil in an oil-bearing stratum vertically thru an annular. section of the stratum around an injection well therein so as t form a solution of the fluid and oil which is produced either thru the annulus or thru the tubing of the well and recycled to the stratum until a substantial annular section of the stratum contains the 'solution of'oil and tluid. During circulation of the solution thru the stratum, the production wells surrounding the injection well are preferably left open to flow so that there is appreciable ow of the 'miscible fluid and solution to a substantial depth into the stratum from the injection well. This creates a larger transition zone where this is desired.

In order to permit vertical tlow or miscible lluid and solution thru an annular section of stratum around the injection well, packers are placed on a tubing string in the well extending to a level adjacent the bottom of the stratum. A lirst packer is set just above the bottom of the stratum anda second packer is placed just below the top of the stratum to provide sections of the stratum below the tirst packer and above the second packer for ingress and egress of fluid. Circulation is effected either thru the annulus into the upper section of the stratum and out the lower section of stratum into the tubing string of vice versa.

i aired States Patent Any'of the fluids of the prior art ranging in viscosity from natural gas to kerosene which are miscible with the.

in-place oil may be utilized in establishing the transition zone. These include in addition to natural gas and kero-- sene, L.P.G., any ofthe normally gaseous light hydrocarbons, garoline boiling range hydrocarbons, etc. Mixtures of these lluids may also be utilized in establishing a transition zone in accordance with the invention. .It is feasible to use one of the heavier fluids for establishing or other relatively cheap gas such as combustion gas.v

Nitrogen may also be utilized.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation in partial section of an arrangement of wells and equipment for effecting the invention, and FIGURE 2 is a partial elevation in partial section of another injection well arrangement for etecting the invention.

Referring to FIGURE l, an oil-bearing stratum 10 is penetrated by an injection well 12 and offset production wells 14. The wells are provided with casings 16 and 18, respectively, which extend thru stratum 10 and are perforated for ingress and egress of fluids. The production wells 14 are provided with tubing strings 20 and injection well 12 contains a. tubing string 22 which extends approximately to the bottom of the stratum. A first packer 24 is set adjacent the lower end to tubing 22 and above the bottom of the stratum. A second packer 26 is positioned on tubing string 22 subjacent the. top of stratum 10. This arrangement allows flow of fluids as indicated by the arrows from the annulus of well 12 generally vertically thru an annular 'section of stratum surrounding this well and into the well below packer 24 for flow up thru the tubing. This illustrates tlow when injection of miscible fluid is thru the annulus with production out thru the tubing. The ilow may be in the reverse order, i.e., thru thev tubing into the bottom of the well and up thru the stratum to the annulus above packer 26, and out of the well.A

A storage tank 30 is connected with casing 16 thru line 32 and with tubing 22 thru line 34 for injection of fluid under the impetus of pump 36. Line 38 connects tubing string 22 with storage tank 30 for tlow of produced Huid when producing thru the tubing. Line 40v connects the well annulus with line 38 for flow of produced fluids when producing thru the well annulus. Pump 42 is positioned in line 38 to assist in ilow of produced fluids to the storage tank 30. Line 44 connects with line 32 for injection of operation in which additional miscible tluid is desired. This line may also connect with a source of driving tluid to be injected to drive the transition zone thru the stratum to produce oil in the production wells.

FIGURE 2 shows a concentric tubing 50 around inner tubing 22 forming an annulus 52 for tlow of lluids to and from the stratum. The casing annulus is packed olf by packer 54. This arrangement is advantageous in deep wells in decreasing the volume of liquid required in the annulus. When using the arrangement of FIGURE 2, lines 32 and 40 connect with annulus 52 or tubing 50.

To start the operation, the selected miscible fluid iS injected eithervthru line 32 or thru line 34. The source of this miscible tluid may be line 44 or a stored supply Assuming that miscible tluid is injected thru the annulus of Well Patented Mar. 31, 1364 miscible tluid at any time during the 12 from line 32, this injected tluid 3 passes thru the perforations in casing 16 above packer 26 into the stratum and, since the least resistance to flow is vertically thru the stratum to the perforations in casings 16 below packer 24, the ow is substantially thru this .path as indicated by the arrows. In passing into the stratum, the miscible fluid mixes and forms a solution with the in-place oil which is produced thru tubing string 22 anddeposited in storage tank 30 for recycling thru line 32 by means of pump 36. As recycling is continued, the'viscosity of the produced uid approaches the viscosity of the in-place oil and the recycling can be terminated at any suitable time with a substantial annular section of the stratum containing the solution.

In this method of setting up the transition zone surrounding well 12 there is a lateral or radial drive of the miscible fluid and solution due to the pressure gradient between well 12 and wells 14 even though wells 14l are not open to flow. In order to increase the size of the transition zone, it is desirable to openwells 14 to ow thru tubing 20. It is inherent in the method o the inven- ,v tion that the outermost section of the transition zone has i a viscosity very closely approaching the viscosity of the in-place oil because of the fact that the concentration of miscible fluid in the deepest penetration thereof is very low and increases toward well 12. Hence, a much more uniformly and gradually varying viscosity gradient is found in the transition zone established by the method of the invention than can be effected by premixing formation oil and miscible tluid above ground and injecting the same into the stratum around an injection well.

After establishing the desired transition zone comprising a solution of oil and miscible fluid of uniformly and gradually increasing viscosity from the injection well out- W'ardly to the outermost area of the desired zone, sometimes called the interface between the transition-zone and 'to remove packers 24 and 26 before .injecting the driving iiuid.

Oil produced in wells 14 by the miscible fluid drive is recovered by conventional means thru tubing 20. Of course, the-process is continued until the miscible duid and transition zone fluid are produced in wells 14 and recovered.

Well 12 may be a central well surrounded by a ring of production wells 14 in a 5, 7, or 9-spot pattern. In the arrangement shown in the drawing, well 12 may be by one injection well in a line of injection wells, while wells 14 are production wells in parallel lines of production wells on either side of a line of wells 12. Other lines of injection wells may flank the lines of production wells 14 on the opposite side from injection wells 12. Propacker on said tubing subjacentthe top of said stratum so as to leave atop section of said stratum above said second packer; injecting a light fluid miscible with the oil in said stratum thru one of said tubing and annulus and thru said stratum intermediate said top and bottom sections to produce a solution of said fluid and oil from said stratum` thru the other of said tubing and annulus; ,recycling said solution thru said tubing and annulus so as to displace more oil from said stratum; and continuing the injection of said fluid and the recycling of said solution until a substantial section of said stratum around said injection well as filled with a solution of oil and said fluid miscible with in-place oil to form said transition zone preparatory to driving with a driving fluid.

2. 'l`he method of claim 1 wherein said miscible fluid 3. The method of claim 1 wherein said miscible fluid is natural gas.

f 4. The method of claim 1 wherein said miscible uid is a mixture of light normally gaseous hydrocarbons.

5. The process of claim 1 wherein said miscible liuid is a mixture of light normally liquid hydrocarbons.

6. The process of claim 1 wherein said at least one production well is open to flow during circulation of luid thru said stratum between the tubing and annulus so as to cause expansion of the transition zone.

7.. The method of claim l wherein said miscible uid is injected thru said tubing and said solution is produced thru said annulus.

8. The method of claim l wherein said miscible Huid is injected thru said annulus and said solution is produced thru said tubing.

9. A process for producing oil from an oil-bearing stratum penetrated by an injection well and at least'ont-I offset production well which comprises establishing a transition zone around said injection well by the method of claim l; thereafter, driving said solution and said transition zone radially outwardly from said injection well toward said at least one production well so as to produce oil therein by injecting a driving fluid into said injection well; and recovering the produced oil from said production well.

10. The process of claim 9 using natural gas as said driving iluid.

1l. The process of claim 9 using normally liquid light ,hydrocarbons as said driving Huid.

v l2. The process of claim 9 using normally gaseous hydrocarbons as said driving Huid.

duction in such a pattern may be elected simultaneously thru the various injection wells or successively.

Certain modications of the invention will become apy parent to those skilled in the art and the illustrative dedrive process in recovering oil from an oil-bearing stratum prior to injection of a driving fluid and forcing same thru v said stratum from said injection well to at least one olset production well, which method comprises providing said References Cited in the le of this patent UNITED STATES PATENTS Spearow Nov. 29, 1955v Allen Oct. 9, 1956 

1. A METHOD OF ESTABLISHING A TRANSITION ZONE DOWNHOLE AROUND AN INJECTION WELL FOR USE IN A MISCLBLE FLUID DRIVE PROCESS IN RECOVERIANG OIL FROM AN OIL-BEARING STRATUM PRIOR TO INJECTION OF A DRIVING FLUID AND FORCING SAME THRU SAID STRATUM FROM SAID INJECTION WELL TO AT LEAST ONE OFFSET PRODUCTION WELL, WHICH METHOD COMPRISES PROVIDING SAID INJECTION WELL WITH A TUBING EXTENDIANG TO A LOWER LEVEL OF SAID STRATUM TO FORM AN ANNULUS WITH THE WALL OF THE WELL; POSITIONING A FIRST PACKER ON SAID TUBING ADJACENT THE LOWER END THEREOF SO AS TO LEAVE A BOTTOM SECTION OF SAID STRATUM BELOW SAID FIRST PACKER; POSITIONING A SECOND PACKER ON SAID TUBING SUBJACENT THE TOP OF SAID STRATUM SO AS TO LEAVE A TOP SECTON OF SAID STRATUM ABOVE SAID SECOND PACKER; INJECTING A LIGHT FLUID MISCIBLE WITH THE OIL IN SAID STRATUM THRU ONE OF SAID TUBING AND ANNULUS AND THRU SAID STRATUM INTERMEDIATE SAID TOP AND BOTTOM SEC- 